Many gas turbines include a compressor, a combustor, and a turbine. The compressor creates compressed air, which is supplied to the combustor. The combustor combusts the compressed air with fuel to generate an air-fuel mixture, which is supplied to the turbine. The turbine extracts energy from the air-fuel mixture to drive a load.
In many cases, the gas turbine includes a number of combustors. The combustors may be positioned between the compressor and the turbine. For example, the compressor and the turbine may be aligned along a common axis, and the combustors may be positioned between the compressor and the turbine at an entrance to the turbine, in a circular array about the common axis. In operation, air from the compressor may travel into the turbine through one of the combustors.
The combustors may be operated at a relatively high temperature to ensure the air and fuel are adequately combusted, improving efficiency. One problem with operating the combustors at a high temperature is that a relatively high level of nitrogen oxides (NOx) may be generated, which may have a negative impact on the environment.
To reduce NOx emissions, some modern gas turbines employ fuel nozzles. For example, each combustor may be supported by a number of fuel nozzles, such as premixed fuel nozzles, which may be positioned in a circular array about the combustor at an entrance to the combustor. During normal operation, the air from the compressor enters the combustor via the fuel nozzles. Within the fuel nozzles the air is “pre-mixed” with fuel to form the air-fuel mixture. The air-fuel mixture is then combusted in the combustor. Pre-mixing the air and fuel permits operating the combustors at relatively lower temperatures, which reduces the NOx produced as a by-product of the combustion process.
Although pre-mixing in the fuel nozzles permits reduced NOx emissions, the fuel nozzles present their own problems. For example, the fuel nozzles may catch fire or retain flame. One common reason for flame in a fuel nozzle is flashback, wherein flame travels backward from the combustion zone of the combustor into the fuel nozzle. Another common reason for flame in the fuel nozzle is auto-ignition, wherein the fuel nozzle independently catches fire due to irregularities in the fuel composition, the fuel flow, the air flow, or the fuel nozzle surface, among others. Regardless of the cause, the fuel nozzle may tend to hold or retain the flame, which may damage the fuel nozzle or other portions of the gas turbine.
So that remedial action may be taken to reduce or eliminate flame in the fuel nozzle, techniques have been developed to detect the presence of flame in the fuel nozzles of the gas turbine. Many of these techniques employ sensors, such as temperature sensors, photon emission sensors, or ion sensors, among others. Typically, a sensor is positioned in each of the fuel nozzles so that flame in any one fuel nozzle may be detected. However, positioning a sensor in each fuel nozzle may be prohibitively expensive, as the turbine may be supported by a number of combustors, and each combustor may be supported by a number of fuel nozzles.
Accordingly, there is a need for systems and methods that detect the presence of a flame in a component of a gas turbine, such as a fuel nozzle of the gas turbine.